How do I write a MAX query with a where clause in JPA 2.0?
criteria, hibernate, jpa, jpa-2.0, max
Solution
There are two ways, one using JPQL, the other using criteria queries. JPQL is simply:
em.createQuery("select max(e.dateProcessed) from Event e where e.org = :myOrg")
.setParameter("myOrg", myOrg)
.getSingleResult();
while using criteria you might have:
CriteriaBuilder qb = em.getCriteriaBuilder();
CriteriaQuery<Number> cq = qb.createQuery(Number.class);
Root<Event> root = cq.from(Event.class);
cq.select(qb.max(root.get("dateProcessed")));
cq.where(qb.equal(Event.get("org"), qb.parameter(MyOrgType.class, "myOrg")));
em.createQuery(cq).setParameter("myOrg", myOrg).getSingleResult();
Problem
I'm using JPA 2.0. Hibernate 4.1.0.Final, and Java 6. How do I write a JPA query from the following psuedo-SQL? ``` select max(e.dateProcessed) from Event e where e.org = myOrg ``` And my domain object looks like the following: ``` @GenericGenerator(name = "uuid-strategy", strategy = "org.mainco.subco.core.util.subcoUUIDGenerator") @Entity @Table(name = "sb__event", uniqueConstraints = { @UniqueConstraint(columnNames={"EVENT_ID"}) } ) public class Event { @Id @Column(name = "ID") @GeneratedValue(generator = "uuid-strategy") private String id; @ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.REMOVE}) @JoinColumn(name = "ORGANIZATION_ID", nullable = false, updatable = true) private Organization org; @Column(name = "DATE_PROCESSED") @NotNull private java.util.Date dateProcessed; ``` I know that CriteriaBuilder.greatest is involved, but I just can't figure out how to write the query. This will return all the event objects that match the organization, but that's as far as I've gotten. ``` final CriteriaBuilder builder = m_entityManager.getCriteriaBuilder(); final CriteriaQuery<Event> criteria = builder.createQuery(Event.class); final Root<Event> event = criteria.from(Event.class); criteria.select(event); criteria.where(builder.equal(Event.get("org"), org)); results.addAll(m_entityManager.createQuery(criteria).getResultList()); ```